1. Field of the Invention
The present invention relates to a charging device for an image forming apparatus, and more particularly, to a charging device for an image forming apparatus which has a charging roller that charges a photoconductive element while being driven by a rotation of the photoconductive element, and a cleaning member made of an elastic member, which cleans a surface of the charging roller contacting thereto during the image forming process.
2. Discussion of the Background
An electrophotographic image forming apparatus is generally provided with a charging device that charges a surface of the photoconductive element. Recently, a charging device that has a charging roller for charging the surface of the photoconductive element by contacting the charging roller thereto has been widely used in place of the older corona discharging-type charging device. This is because the charging roller produces less ozone than the corona discharging-type device.
Such a contact-charging type charging device which performs a charging operation with the charging roller contacting the photoconductive element may cause an insufficient charge due to the adhesion of residual toner remaining on the photoconductive element, after the image on the photoconductive element is transferred to a transfer sheet to the photoconductive element.
In order to avoid an occurrence of insufficient charge due to the adhesion of residual toner in the charging device, a cleaning member made of, for example, a sponge or the like is configured to contact a surface of the charging roller with such an appropriate pressure that the contacting portion of the cleaning member is deformed. Thereby, the charging roller is rubbed at the surface thereof with the cleaning member when rotating. As a result, toner, paper powder and the like which adhere on the surface of the cleaning roller are removed (as described in, for example, Japanese Laid-Open Patent Publication No. 272594/1990).
However, when the charging roller is cleaned at its surface with such an elastic cleaning member, the cleaning member is deformed toward the rotating direction of the charging member due to a friction force caused by the contact of the cleaning member with the rotating photoconductive element. If the friction force is excessively large, a further problem may be caused in which the cleaning member may be peeled off or may fall off a supporting member that supports the cleaning member with an adhesive.
In addition, a contact area between the cleaning member and the charging roller may vary due to the distortion of the cleaning member toward the rotating direction of the charging roller. This variation of the contact area of the cleaning member with the charging roller may thereby vary a friction load which is added to the charging roller from the cleaning member. Consequently, the rotational speed of the charging roller may become erratic. Furthermore, when the charging roller is rubbed at the surface thereof with the cleaning member to an excessive extent, the charging roller may cause a so-called "filming phenomenon" in which the toner accretes to the surface of the charging roller by heat.